# The hockey-stick stock recruitment function Calculates the number of recruits as given by the hockey-stick stock recruitment function. ```r rec_hockey(SSB, rec_args) ``` ## Arguments - `SSB`: A numeric value representing the Spawning Stock Biomass (SSB) of a given species (g). - `rec_args`: A list object of length `nfish`, with each element in the list including a value of `a` and `b` for each species. `a` is a positive numeric value, often referred to as the **density-independent** parameter. The default is 1. `b` is a positive numeric value, often referred to as the **density-dependent** parameter. The default is 0.001. ## Returns A numeric value representing the number of recruits of a given species. ## Details The stock recruitment function is defined as `min(a*(SSB/1e9), b)`. ## Examples ```r # Set up the inputs to the function - species-independent parameters nfish <- nrow(NS_par) nsc <- 32 maxsize <- max(NS_par$Linf)*1.01 # the biggest size is 1% bigger than the largest Linf l_bound <- seq(0, maxsize, maxsize/nsc); l_bound <- l_bound[-length(l_bound)] u_bound <- seq(maxsize/nsc, maxsize, maxsize/nsc) mid <- l_bound+(u_bound-l_bound)/2 # Set up the inputs to the function - species-specific parameters Linf <- NS_par$Linf # the von-Bertalanffy asymptotic length of each species (cm). W_a <- NS_par$W_a # length-weight conversion parameter. W_b <- NS_par$W_b # length-weight conversion parameter. k <- NS_par$k # the von-Bertalnaffy growth parameter. Lmat <- NS_par$Lmat # the length at which 50\% of individuals are mature (cm). # Get phi_min tmp <- calc_phi(k, Linf, nsc, nfish, u_bound, l_bound, calc_phi_min=FALSE, phi_min=0.1) # fixed phi_min phi_min <- tmp$phi_min # Run calc_ration_growthfac() tmp <- calc_ration_growthfac(k, Linf, nsc, nfish, l_bound, u_bound, mid, W_a, W_b, phi_min) sc_Linf <- tmp$sc_Linf wgt <- tmp$wgt # Calculate maturity mature <- calc_mature(Lmat, nfish, mid, kappa=rep(10, nfish), sc_Linf) # Create recruitment functions stored_rec_funs <- get_rec_fun(rep("hockey-stick", nfish)) recruit_params <- do.call("Map", c(c, list(a=NS_par$a, b=NS_par$b))) # Get an initial population N0 <- get_N0(nsc, nfish, mid, wgt, sc_Linf, intercept=1e10, slope=-5) # Calculate the SSB SSB <- calc_SSB(mature, N0, wgt) rec_hockey(SSB[1], recruit_params[[1]]) ``` ## References Barrowman, N.J., Myers, R.A. (2000). Still more spawner-recruit curves: the hockey stick and its generalisations. **Canadian Journal of Fisheries and Aquatic Science**, 57:665–676. Thorpe, R.B., Le Quesne, W.J.F., Luxford, F., Collie, J.S., Jennings, S. (2015). Evaluation and management implications of uncertainty in a multispecies size-structured model of population and community responses to fishing. **Methods in Ecology and Evolution**, 6:49-58. ## See Also `calc_recruits`, `make_rec_fun`, `get_rec_fun`, `rec_BH`, `rec_Ricker`, `rec_const`, `rec_linear` and `calc_SSB`

rec_hockey function